Background: Non-melanoma skin cancer is the most common malignant tumor in humans. The role of ultraviolet radiation is well-known in the pathogenesis of basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). CD10 is a zinc-dependent metallopeptidase known as common acute lymphoblastic leukemia antigen (CALLA). Although CD10 expression has been investigated in some cutaneous tumors, to our knowledge, data regarding its expression in cutaneous epithelial neoplasms are very limited. In this study, we aimed to determine the immunohistochemical expression of CD10 in BCC and SCC and to find whether it could distinguish between these two skin malignancies. 

Methods: Twenty SCC and 42 BCC cases were retrieved randomly from Ayatollah Rouhani Hospital pathology archive and CD10 expression was determined in tumoral and stromal cells of each case based on immunohistochemical method. Positive CD10 staining was identified as brown cytoplasmic, with or without cell membrane staining.

 Results: In all the 20 SCC cases, tumor cells failed to stain with CD10 in contrast to the stromal cells that showed CD10 expression in 18 cases (90%). In BCC cases, the expression of CD10 was noted in tumor cells in 25 cases (59.5%) and in stromal cells of 32 cases (76.2%). There was no relation between CD10 expression in aggressive and non- aggressive BCC. 

Conclusion: Our findings suggest that CD10 is a useful immunohistochemical marker to differentiate between BCC and SCC. At least, if tumor cells were CD10 positive, this would favor BCC over SCC. Due to small number of aggressive BCC in contrast to non- aggressive types, more studies need to be done to prove or rule out this finding.